NEW YORK — Reports of Americans living beyond the ripe old age of 100, it appears, were greatly exaggerated.

The Census Bureau predicted six years ago that the country would be home to 114,000 centenarians by 2010. The actual number was 53,364, the census reported recently. That represented an increase of 5.8 percent since 2000, compared with a 9.7 percent gain in the nation’s population as a whole.

The figures challenged assumptions that increasing life expectancy will mean more U.S. residents living into their 100s. The oldest human, who lived to 122, died back in 1997: Jeanne Louise Calment sold canvas to Van Gogh at her family’s fabric store in Arles, France.

“Here we have 6.9 billion people and no one has come close, survival-wise, to this one lady almost 15 years ago,” said Tom Perls, director of the New England Centenarian Study at the Boston University School of Medicine. “That should give you an indication of how incredibly rare it is. We really are hitting a plateau.”

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The census numbers on centenarians, which remain the object of much dispute among demographers, don’t suggest that more people aren’t living longer. Life expectancy increased from 51.5 years for a man born in 1900 to 80.1 years for a man born in 2001, according to the Social Security Administration. Results from the recent census showed that those aged 90 to 94 and 95 to 99 increased 30.2 percent and 29.5 percent.

Rather, some demographers and researchers say the century mark may just be tougher for humans to reach than previously imagined.

“The likelihood that we will continue to increase the proportion of centenarians is not great, not at all,” Leonard Hayflick, a professor of anatomy at the University of California, San Francisco, said in an interview. “It’s probably contrary to most people’s thinking because of the hype that has grown up around this field in the last 20 years.”

Hayflick, 83, challenged the notion in 1961, when he discovered what is now known as The Hayflick Limit — that cells age as they divide only a fixed number of times.

The population of centenarians showed major gains in the last century. In 1950 there were just 2,300 people estimated to be 100 and older. The number jumped 35 percent in 2000 to 50,454, from 37,306 in 1990.

Census officials predicted that those gains would continue, though in 2009 they lowered their previous estimate to 64,024. Even that projection was high, so the figures have them reconsidering their assumptions. The number of men older than 100 even decreased 8.9 percent.

“When we put out the projections, that is something that people voiced concerns about,” said David Waddington, chief of the population projections branch at the census bureau. “It is something that we will be looking at.”

Not everyone was disappointed by the news.

“I don’t want to live to 100,” said Bill Zuk, 50, a customer-service representative for the finance publication The Deal, as he left the New York Sports Club on Wall Street last week. “I have an aunt that is 94, and that’s enough to see. I’d be satisfied with 80.”

Keith Petensky, 35, a real estate lawyer from Bedford, N.Y., said living into his 100s only sounded good if he were healthy.

“You can get pumped up with all sorts of drugs, but at the end of the day nature is nature and you can’t beat nature,” he said. “You can’t beat God.”

Many demographers, including those at the Census Bureau, base their projections on the assumption that life expectancy will increase indefinitely. Hayflick called that idea “nonsense” because the technological gains made during the 1900s are one-time improvements in health that can’t be duplicated.

“In 1900, very few people had in-house toilets and bathing facilities,” said Hayflick, whose own mother is 105.

Counting centenarians has been a tricky business. Birth records were poor at the turn of the last century, when those now turning 100 were born. Demographers also have found that people are more inclined to inflate, rather than deflate, their age. The census bureau doesn’t disagree.

“We have a long history of data-quality issues with centenarian data,” said Julie Meyer, a demographer with the bureau.

The difficulty in counting has led some experts to conclude that humans are nowhere near the limits of longevity.

“The U.S. did not have mandatory birth records until about 1940,” said Steven Austad, a professor of biogerontology at the University of Texas Health Science Center in San Antonio. “This is just a sorting out of bad birthing information from earlier censuses.”

Centenarians have long been seen as keys to giving people clues about how to live healthier lives. Many of them report that they simply enjoyed life as it arrived, researchers say.

Ebby Halliday, 100, the founder of Ebby Halliday Realtors in Dallas, drove to work every day until six months ago.